1. Field of the Invention
The present invention relates to control of vibration type driving apparatus for applying a cyclic signal to an electro-mechanical energy conversion element such as an electrostrictive device or a piezoelectric device to induce vibration of a vibrator and drive a driven body by use of this vibration, and to an apparatus such as a video camera or a lens for video camera using the vibration type driving apparatus as a driving source.
2. Related Background Art
There are known systems using a DC motor as a driving motor for focus, zoom, iris diaphragm, extender, macro, and so on in the video camera or in the lens for video camera.
FIG. 5 illustrates a control system of a video camera lens using the conventional DC motor. In this control system a position detector 206 detects information of a real position of lens 205 and the information of real position is input into a position comparator 202. The position comparator 202 compares the real position of lens 205 detected, with a target position supplied from a command signal generator 201 and supplies a control signal to zero a difference between them to a motor driving circuit 203. When this control system is used for focusing, the command signal generator 201 is a potentiometer for detecting a focus control amount given by a cameraman, which supplies the target position (focus demand) ranging from nearest to infinity, to the position comparator 202. Then the motor driving circuit 203 applies a driving signal according to the control signal to the DC motor 204 to drive the lens 205 toward the target position.
In the above control system using the DC motor, however, when the target position is altered on the way of driving of the lens toward the target position, particularly when a new target position is a position which the lens has already passed, the driving direction of the lens has to be inverted. At this time the motor is reversed by inverting the polarity of the driving signal applied to the DC motor. Some time is necessary for actual inversion of rotating direction of the motor after the inversion of the polarity of driving signal, because of the inertia of the motor. This poses a problem that the system fails to follow quick inversion manipulation of focus demand conducted by the cameraman.